Chippers are used to reduce branches, trees, brush, and other bulk wood products into small chips. Chippers typically include a feed chute, one or more feed rollers, a chipping mechanism, and a drive system for powering feed rollers and the chipping mechanism. Through the operation of the feed rollers, products to be chipped are brought into contact with the chipping mechanism, which grinds, flails, or cuts the wood products into small pieces. The performance of a chipper is in part dependent on the ability of the feed rollers to continually grab and pull the materials to be chipped from the feed chute into the chipper.
A known feed roller configuration includes two opposed feed rollers that can be moved towards or away from each other. Such feed rollers are configured so that the distance between the feed rollers varies to accommodate the differences in the sizes of the materials to be chipped. The force that directs the feed rollers towards each other can affect the ability of the feed rollers to pull materials to be chipped into the chipper. For example, if the force directing the feed rollers together is too small, the rollers may slip along the surface of a large, heavy log and fail to pull the log into the chipper. If the force is too large, it can cause the material to be chipped to jam instead of feed. Accordingly, a constant force system is not ideal. In addition, a system that can be turned on and off automatically can be advantageous.
Several systems for applying a variable force to direct the feed rollers together are known. Some such systems utilize springs, while others incorporate hydraulic fluid pressure. See, for example, U.S. Pat. No. 6,357,684 to Morey; U.S. Pat. No. 3,955,765 to Gaitten; and U.S. Pat. Pub. 2003/0111566 to Seaman et al. The controllability of spring systems is limited, and efficiency and effectiveness of existing hydraulic systems can be improved upon.